1. Field of the Invention
The present invention relates to a probe microscope and, more specifically, to a probe microscope having an observation optical system for observing a measured object.
2. Description of the Related Art
In the related art, a probe microscope including a cantilever having a probe that comes into contact with a measured object, a displacement detecting optical system configured to detect a displacement of the cantilever, and an observation optical system for observing the measured object, and being configured to observe a surface geometry of the measured object by scanning a surface of the measured object with the probe and detecting the displacement of the cantilever, which swings according to the surface geometry of the measured object is known (for example, see Japanese Unexamined Patent Application Publication No. 6-160077).
According to the probe microscope as described above, the displacement detecting optical system includes a first light source configured to irradiate the cantilever with light and a displacement detecting unit configured to detect a displacement of the cantilever by receiving the light emitted from the first light source and reflected from the cantilever. The observation optical system includes a second light source configured to irradiate the measured object with light and an image forming lens configured to form an image of the light emitted from the second light source and reflected from the measured object to a predetermined position. An observing unit is configured to be used for observing the measured object by receiving the light imaged by the image forming lens.
The probe microscope includes the cantilever and an objective lens disposed between the first light source and the second light source. The objective lens is used commonly by the displacement detecting optical system and the observation optical system.
The objective lens is designed and arranged so as to have a focal point at a position of the cantilever in order to cause the cantilever to be irradiated with the light emitted from the first light source and to allow the light applied to the cantilever to be observed by the observing unit.
However, since the measured object is located at a position apart from the cantilever by a distance corresponding to the probe, problems are created. Since the objective lens is designed and arranged so as to observe the light applied to the cantilever by the observing unit, the measured object cannot be observed adequately by the observing unit when determining the position of measurement.
Here, arranging the measured object at a position in the proximity of the focal point of the objective lens by bringing the cantilever and the measured object in proximity to each other is contemplated. However, if the cantilever is moved when determining the position of measurement, the probe and the measured object may come into contact with each other, which may cause damage to one or both of the probe and measured object. Removing the cantilever when determining the position of measurement or the like and mounting the cantilever again after the determination of the position of measurement is also contemplated. However, removing and re-mounting the cantilever may result in undesirable displacement of the cantilever.
As a countermeasure for these problems, according to the probe microscope described in Japanese Unexamined Patent Application Publication No. 6-160077, the measured object is adequately observed by the observing unit by adjusting a distance between the image forming lens and an image-pickup device (observing unit) when observing the measured object.
FIGS. 8A-8B schematically illustrate a configuration of a probe microscope 100 in the related art.
The probe microscope 100 includes a cantilever 110 having a probe 111 that comes into contact with a measured object W, a displacement detecting optical system 120, an observation optical system 130, a half mirror 140, and an objective lens 150, so that the surface geometry of the measured object W is observed by scanning the surface of the measured object W by the probe 111 and detecting the displacement of the cantilever 110 swinging according to the surface geometry of the measured object W.
The displacement detecting optical system 120 includes the half mirror 140, and includes the first light source and a displacement detector 121 as the displacement detecting unit.
The observation optical system 130 includes the half mirror 140, and includes an incident-light lighting device (not shown) as the second light source, an image forming lens 131, and an image-pickup device 132.
The half mirror 140 has a function to reflect the light emitted from the displacement detector 121 to be applied to the cantilever 110, and guide the light reflected from the cantilever 110 to the displacement detector 121. The half mirror 140 also has a function to apply the light emitted from the incident-light lighting device to the measured object W, and guide the light reflected from the measured object W to the image forming lens 131 and the image-pickup device 132.
When irradiating the cantilever 110 with the light emitted from the displacement detector 121 and observing the light applied on the cantilever 110 by the image-pickup device 132, an optical path of the displacement detecting optical system 120 and the observation optical system 130 runs as shown in a solid line in FIG. 8A. In this case, the light reflected from the cantilever 110 forms a parallel luminous flux via the objective lens 150, and forms an image at a position of the image-pickup device 132 arranged at a focal point of the image forming lens 131. Therefore, the image-pickup device 132 is able to observe the light applied on the cantilever 110 adequately.
However, as shown in double-dashed chain lines in FIG. 8A, the light reflected from the measured object W forms a condensed luminous flux via the objective lens 150, and hence forms an image at a position different from the position of the image-pickup device 132 which is arranged at the focal point of the image forming lens 131. Therefore, the image-pickup device 132 is not able to observe the measured object W adequately.
Accordingly, according to the probe microscope 100, as shown in FIG. 8B, the measured object W is adequately observed by the image-pickup device 132 by adjusting the distance between the image forming lens 131 and the image-pickup device 132 by a distance L.
However, in the probe microscope 100 described in Japanese Unexamined Patent Application Publication No. 6-160077, a driving mechanism for driving the image-pickup device 132 along an optical axis of the image forming lens 131 is required, and hence there is a problem that the probe microscope 100 must increase in size. Also, since adequate adjustment of the distance L every time when the object to be observed by the image-pickup device 132 (the cantilever 110 and the measured object W) is required, there is a problem such that the configuration of the probe microscope 100 is complicated.